A test of fluctuating asymmetry as a bioindicator of stress in antlered flies

Abstract

Disturbances to the developmental processes of organisms produce phenotypic asymmetries. It has been hypothesized that populations subjected to sustained environmental stress will suffer greater developmental instability and, therefore, exhibit greater morphological asymmetry than healthy populations. Thus, sampling the average asymmetry of populations through time might be a useful indicator of the overall health of their corresponding habitat. This hypothesis was investigated using antler flies (Phytafmia spp.) in Papua New Guinea rainforests. The larval substrate of these flies is restricted to a few rainforest tree species found in primary forests. The prediction that fly populations in logging areas would exhibit greater asymmetry was tested by comparing fluctuating asymmetry (FA: small, random deviations from perfect symmetry) of fly populations in primary forest and logging areas, as well as from a single location across time. Only one (P. biarmala) of three species had significantly higher FA (according to a composite measure of wing venation) at logged sites than at intact forest sites, and the average FA decreased in a population of P. afcicornis over a 20-year period despite continuous logging in the area. Because some sample sizes were unavoidably small, a meta-analysis of combined effect sizes was performed and revealed a significant effect of habitat on FA across the species. Logging practices may impose stress on these flies as alleged, but if so the indication of the stress through FA levels was weak. Thus, reliance on this method as a monitoring tool for this environment should be considered with caution.